In the practice of dressing and preparation, use is made of, inter alia, strainer bends and centrifugal strainers for the same purpose. In the case of the strainer bend, as a rule, the suspension flows over an overflow weir in a thin layer onto the strainer from a height of about 460 m. This height produces a charging velocity of about v=3 m/s. In the case of the centrifugal strainer, the suspension is charged via a nozzle at high velocity tangentially into a large, horizontal ring. The latter consists of a U-shaped, inwardly open channel, the rear of which is formed by the strainer lining, which runs spirally narrower. The substantially dewatered material subsequently reaches a conical straining basket for post-dewatering, DE-A 35 15 891.
At the high charging velocity (v=7-8 m/s) a considerable centrifugal force is generated, by which a segregation of the suspension takes place. Since the solid is generally heavier than the liquid, it accumulates on the outside of the straining area. After one revolution, virtually only the preliminarily cleaned liquid flows off downward, whereas the solid remains in circulation on the strainer. Fresh charging causes the layer of solid to become thicker and thicker. This has the effect of an increase in the flow resistance for the liquid phase through the strainer, i.e. a reduced dewatering efficiency, and of an increased wear of the straining elements.